AB1429 EMAPALUMAB TREATMENT FOLLOWED BY HEMATOPOIETIC STEM CELL TRANSPLANTATION IN SYSTEMIC JUVENILE IDIOPATHIC ARTHRITIS COMPLICATED BY RECURRENT MACROPHAGE ACTIVATION SYNDROME
Authors: C. Bracaglia, M. Pardeo, G. Marucci, S. Riccio, F. Quagliarella, I. Caiello, G. Prencipe, P. Merli, F. Locatelli, F. De Benedetti
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Macrophage activation syndrome (MAS) is a life-threatening complication of different rheumatic diseases, particularly of systemic juvenile idiopathic arthritis (sJIA). <h3>Objectives</h3> We report the case of 17-year-old girl with sJIA complicated by recurrent severe MAS episodes. <h3>Methods</h3> Patient received emapalumab (anti-IFNg antibody) in two subsequent MAS episodes, then underwent an uncomplicated hematopoietic stem cell transplantation (HSCT) from a haploidentical donor, while receiving emapalaumab and anakinra granting complete control of inflammatory activity of the underlying disease. One year after transplant she is in complete disease remission. <h3>Results</h3> A 13-year-old Caucasian girl presented with fever, rash and hepato-splenomegaly. Laboratory parameters were consistent with full-blown MAS (tab 1). In the absence of clear evidence of an underlining condition, a diagnosis of secondary HLH was made. Treatment with high dose of intravenous (IV) methylprednisolone (mPDN) and oral cyclosporine (CYC) was started with progressive improvement. After one year, still on CYC, she presented with fever, rash and arthritis with laboratory parameters consistent with MAS (table 1), diagnosis of sJIA complicated by MAS was made. In 24 hours, her general condition rapidly worsened and she was admitted to the ICU. High dose of IV mPDN (7 pulses of 30 mg/kg/day) as well as IV CYC (5 mg/kg/day) did not yield a response. Emapalumab was started, in the NI-0501-06 trial, (6 mg/kg initial dose followed by 3 mg/kg every 3 days) for 11 infusions. Conditions progressively improved. In order to prevent flares of the underlining sJIA, anakinra (2 mg/kg/day) was started. After 2 years in clinical remission, while she receiving anakinra every other day, she presented with fever, vomiting and diarrhea. Anakinra was immediately increased to daily dosing. Stool analysis showed Salmonella infection and antibiotic therapy was started. Her condition rapidly worsened, laboratory parameters were again consistent with full-blown MAS (tab 1). She required ICU admission for multiorgan failure. Anakinra was administered IV and the dose increased up to 12 mg/kg/day. IV MPDs (8 pulses of 30 mg/kg/day) as well as IV CYC (5 mg/kg/day) were started with partial response. Based on her previous response, emapalumab was started again (compassionate use) with marked and rapid improvement. Because of recurrent MAS episodes, particularly for their rapidly progressive evolution, the patient underwent an ex-vivo T cell-depleted haploidentical HSCT from her mother. The conditioning regimen was based on a Thiotepa-Treosulfan-Fludarabine scheme. Emapalumab was continued 1 month after HSCT together with anakinra. The patient developed mild complication, achieved full donor engraftment with complete donor-derived immune reconstitution after 3 months. One year after HSCT, the patient is in excellent clinical condition on anakinra every other day, with complete remission of sJIA/MAS, also confirmed by persistently normal levels of IL-18 and CXCL9 (tab 1). <h3>Conclusion</h3> This case provides further evidence of the efficacy of emapalumab in MAS [1], of the potential benefit of HSCT in difficult sJIA patients [2]. Notably, full control of inflammatory activity with emapalumab and anakinra may help to obtain a successful HSCT and reduce the risk of rejection. <h3>References</h3> [1] De Benedetti F. Ann Rheum Dis 2022-eular.803 [2] Morelle G. Pediatr Rheumatol Online J 2021 Mar 12;19(1):27 <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> Claudia Bracaglia Speakers bureau: SOBI, Consultant of: SOBI, Novartis, Manuela Pardeo Consultant of: SOBI, Giulia Marucci: None declared, Simona Riccio: None declared, Francesco Quagliarella: None declared, Ivan Caiello: None declared, Giusi Prencipe: None declared, Pietro Merli Consultant of: SOBI, Franco Locatelli Consultant of: SOBI, Fabrizio De Benedetti Consultant of: Abbvie, SOBI, Novimmune, Novartis, Roche, Pfizer.